The present invention relates to a directly heating fixing apparatus, which, in an image forming unit such as an electronic picture copying machine, facsimile, printer or the like, performs the fixing of images by passing a paper carrying non-fixed images between a pair of rolls.
Conventionally, to fix an image made of toner which is formed on a copying sheet such as a zinc oxide sensitized paper, ordinary paper, plastic sheet or the like, there is known a heating type fixing apparatus which has a heating roll and a pressurizing roll made to contact with each other under pressure and which heats and applies a pressure to a sheet to be copied by passing it between those rolls. In a conventional heating type fixing roll, a heat source such as a halogen lamp, nichrome wire or the like is provided inside of the heating roll, so that, by the radiation of the heat source, the heating roll may be heated.
However, in such heating method, time required until the surface of the heating roller has reached a predetermined temperature, e.g. 180.degree. C. (warm up time) has been on the order of several minutes, which is a relatively long time.
Recently, to shorten the warm up time, the so-called directly heating type fixing apparatus has been proposed. In Japanese Patent Appln. Laid-Open No. 164860/1980, there is disclosed a heat emission roller in which a heat insulating layer, insulating layer, heat generating resistance layer and a protection layer are sequentially formed about a core bar. At both ends of the heat generating roller are provided electrically conductive members which are connected with the heat generating resistance layer via electrical conductors, and a plurality of arcuate sliding terminals are made to contact the electrically conductive members under pressure by means of a spring. Reduced diameter portions at both ends of the core bar are rotatably supported by means of bearing units. In such a construction as above, however, since the sliding terminals and the bearing units are separately provided, when an effective fixing width of the fixing apparatus is assumed to be constant, the overall length of the apparatus cannot but be enlarged. The above-mentioned disadvantage is serious, in view of the recent demand that the entire apparatus must be made compact.
In Japanese Patent. Appln. Laid-Open 161768/1982, a heat generating roller has been disclosed, wherein an insulating layer and a heat generating layer are sequentially formed on the outer periphery of a cylindrical body, and in which sliding rings electrically connected with the heat generating layer are provided at both ends of the roller. Sliding brushes are made to contact sliding rings under pressure, so that the current required for heating may be supplied. Though, in this heating roller, no bearing is explicitly shown, from the provision of a rotary shaft, it is considered that bearings are engaged with the rotary shaft. The above construction also exhibits the disadvantage that the heating roller is elongated by the amount of length needed for providing the bearing and the electrode portion separately. Furthermore, in this heating roller, since the area of contact between each sliding brush and the associated sliding rings is small, problems related to wearing or bad contacts tend to arise.
Furthermore, in Japanese Patent Appln. Laid-Open No. 91376/1985, sliding members for feeding current are provided in the interior of bearings which support both ends of a heating roller. In this construction, however, the structure of each bearing is complicated and is not suited for practical use.
Co-pending U.S. patent application Ser. No. 837,178 on Mar. 7, 1986, which has been assigned to the same assignee as that of the present application, is also directed to a directly heating fixing apparatus of the type as discussed in the present application.